Method of cleaning a stream of coke oven gas and apparatus therefor



E. F. SCHON 3,451,896 F CLEANING A STREAM OF COKE OVEN GAS METHOD 0 IJune 24, 1969 AND APPARATUS THEREFOR Filed April 7, 1967 QD UVEE m932min NA KMAOOU mwkss mom xz vm 22E. QZCZQUMQ INVENIOR ERICH KF. SCHONUnited States Patent Olfice Patented June 24, 1969 US. Cl. 201--15Claims ABSTRACT OF THE DISCLOSURE Method of cleaning a stream of cokeoven gas containing ammonia therein comprising: dividing the stream ofcoke oven gas into a first stream for subsequent combustion in coke ovenheating fines and a second stream for subsequent conversion to wastegases which are vented to the atmosphere, scrubbing the first streamwith aqueous media to cleanse the gas and remove ammonia therefrom so asto form aqueous ammonia liquor, and passing the cleansed first stream tothe heating lines and burning it therein to provide heat for destructivedistillation of coal in the coke oven coking chambers. Methodadditionally contemplates distilling the aqueous ammonia liquor to formammonia vapor, admixing the ammonia vapor with the second stream of cokeoven gas, and passing the ammonia-rich second stream to a conversionzone and converting the stream to waste gas. Apparatus for effecting theforegoing method is also described.

BACKGROUND OF THE INVENTION Field of the invention Description of theprior art By-product coke ovens of the foregoing type are, of course,well known in the art. The coke oven gas coming from such by-productovens contains various contaminants, in particular, ammonia, H S, HCN,CO tars, benzols, phenols, and the like. Heretofore, it has beenconventional to recover one or more of the foregoing components, e.g.,ammonia, and then to sell such recovered product so as to olfset thecost of operating the coke oven. However, the expenses involved ineffecting such recovery have been increasing, so much so that as of thepresent time the recovery costs tend to exceed the commercial value ofthe products so recovered.

It has been conventional in the recovery of ammonia from coke oven gas,to react it with an acid such as sulfuric acid, phosphoric acid, or thelike, so as to obtain ammonium sulfate or ammonium phosphate, whichproducts can then be sold as fertilizers. Here too, the cost of recoveryas fertilizers has tended to exceed the commercial value of suchfertilizers.

SUMMARY OF THE INVENTION 'In accordance with the present invention, amethod is provided for cleaning a portion of a stream of cake oven gascontaining ammonia and other contaminants therem,

whereby the cleansed portion is subsequently combusted in coke ovenheating fines so as to provide heat for the coking of coal disposed inthe coking chambers of the coke oven. The ammonia and other contaminantsthat are removed from the cleansed portion are passed to the second(uncleansed) portion of coke oven gas, and this portion is converted towaste gases that are essentially non-pollutants, which gases are ventedto the atmosphere.

BRIEF DESCRIPTION OF THE DRAWING My invention will best be understoodfrom the following detailed description taken in conjunction with theaccompanying drawing, which is a schematic flow sheet of the method andapparatus of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with one aspectof my invention, I have developed a method of cleaning a stream of cokeoven gas typically containing ammonia, H 8, HCN, CO tars, benzols,phenols, and other contaminants therein, this gas having been obtainedfrom a coke oven battery cornprising a plurality of spaced apart cokingchambers with a plurality of heating walls disposed therebetween, theheating walls each having therein a plurality of heating cues. My methodinvolves dividing the stream of coke oven gas into a first stream forsubsequent combustion in the coke oven heating flues and a second streamfor subsequent conversion to waste gases which are vented to theatmosphere. The first stream is scrubbed with aqueous media to cleansethe gas and remove ammonia and other contaminants therefrom, therebyforming an aqueous ammonia liquor. The so cleansed first stream is thenpassed to the heating flues of the coke oven and burned therein so as toprovide heat for destructive distillation (coking) of coal in the cokingchambers.

My method additionally contemplates distilling the aqueous ammonialiquor to form ammonia vapor, admixing the ammonia vapor with the secondstream of coke oven gas, and passing the resulting ammonia-rich secondstream to a conversion zone and converting this stream to waste gas thatmay be vented to the atmosphere without danger of pollution.

Desirably, the amount of coke oven gas employed in the first stream isslightly in excess of the heating requirements for the heating fines ofthe coke oven battery. Thus, after the first stream has been cleansed,that amount of gas in excess of the heating requirements for the heatingflues may be bled oif and admixed with the second stream prior to itsconversion to waste gases.

Advantageously, the first stream, prior to the scrubbing step, is spraycooled with ammoniacal liquor so as to remove some or all of the tarsand water vapor to thereby form tar-containing aqueous ammonia liquor.Such liquor may then be admixed with the aqueous ammonia liquor obtainedas a result of the subsequent scrubbing step. My method also providesfor removing any tars contained in the aqueous ammonia liquor obtainedby virtue of the aqueous spray cooling, prior to the admixing of suchaqueous ammonia liquor with the aqueous ammonia liquor obtained from thescrubbing step.

Referring to the second stream of coke oven gas that is ultimatelyconverted to waste gases, it is desirable that this stream be heatedprior to the admixing therewith of the ammonia vapor obtained from. thefirst stream, the heating being to such temperature that upon admixing,any water or tars that may be present in the ammonia vapor do notcondense.

Referring to the drawing, reference numeral 10 designates the coke ovenbattery, which includes a plurality of spaced apart coking chambers witha plurality of heating walls disposed therebteween, the coking chambersand heating walls generally designated by the reference numeral 12. Cokeoven regenerators 14, for preheating air prior to its introduction intothe combustion chambers, are disposed beneath the coke oven chambers andheating walls 12 in conventional fashion.

As coal in the coking chambers is coked, coke oven gas is evolved. Thecoke oven gas is conducted, via conduit 16, through cooling chamber 18to juncture 20, wherein it is divided into two streams, a first stream Stypically 45% by volume of the coke oven gas, which stream is to becleansed and then utilized as fuel in the coke oven heating flues, and asecond stream S typically 55% by volume, for subsequent conversion towaste gases.

The first stream S is passed via conduit 24 into spray cooler 26 forremoval of some of the tars and water therefrom as describedhereinafter. The cooled gas stream S now passes via conduit 28 to tarfilter 30. The tar filter, which desirably is electrical, effectsseparation of any residual tars. These tars are drawn off via conduit 31and passed to decanting tank 50. The gas stream S is then passed viaconduit 32 and blown by exhaust fan 34 through conduit 36 into scrubber38. Fresh water is fed into spray head 40 of the scrubber via pipeline42. The spray scrubber 38 serves to remove ammonia from the coke ovengas.

The cleansed gas stream S is then passed via conduit 44 into gasdistribution channel 46 of the coke oven 10. Air is introduced to theregenerators via conduit 47 for preheating and is then admixed with thecleansed gas in conventional manner for combustion in the coke ovenheating flues. The thus combusted gases pass from the regeneratorsthrough conduit 49 to stack 51 and are vented to the atmosphere.

Referring again to spray cooler 26, this serves to remove some tars andwater from the first stream S of the coke oven gas. The bottoms water,which contains therein tars and ammonia, is divided into two portions.One of these portions is drawn off the bottom of spray cooler 26, passedthrough conduit 59, cooled by cooler 61, and recycled through spray head63.

The other portion is removed via conduit 48 and pumped into flushingliquor tank 118.

Ammonia-containing water (flushing liquor) is drawn from tank 118 viaconduit 120 and pumped through spray nozzles 122 into conduit 16 (standpipe) and into cooling chamber 18. Chamber 18 collects the gases fromthe individual coking chambers and hence serves as a gas collectingmain. As the hot gases contact the flushing liquor some of the liquorwill evaporate, thereby cooling the hot gases. The rest of the flushingliquor together with the gases flows through conduit 19 and passes viaconduit 124 to tank 118. Solid particles settle to the bottom and areremoved from the liquor (not shown).

The surplus of ammonia-containing water and tars, representing thequantities produced in the coking chambers, is removed via conduit 1%and passed to decanting tank 50. Tars are removed from the bottom oftank 50 via conduit 52, and may either be pumped via conduit 54 to steamboiler 56 for ultimate conversion to waste gas or, alternatively, may bepassed through conduit 58, collected, and sold.

Aqueous ammonia liquor is collected from the top of decanting tank 50and pased through conduit 60 to a suitable dephenolizing apparatus 62,e.g., an extractor, with the separated phenols being collected viaconduit 64. The phenols may be readily extracted in dephenolizingapparatus 62 by means of benzene or other appropriate solvent.

Aqueous ammoniacal liquor from the bottom of dephenolizing apparatus 62is passed via conduit 66, along with aqueous ammoniacal liquor from thebottom of scrubber 38 via conduit -70, to distilling column 72. Heat issupplied to distilling column 72 in the for-m of steam from steam boiler56 via conduit 74. Ammonia vapor coming off the top of distilling column72 is rectified by indirect cooling in rectifier 76, the cooling waterto the rectifier being suplied via conduit 78 and being returned viaconduit 80. Dephenolized waste water is withdrawn from the bottom ofcolumn 72 via conduit 82 and may be discharged.

In order to reduce the requirements (1) of fresh water, supplied viaconduit 42 and (2) of steam, supplied via conduit 74, aqueous ammoniacalliquor leaving dephenolizing apparatus 62 via conduit 66 may be passed,in whole or in part, via conduit '67 and pumped into the liquor recycledvia conduit 109, before such liquor passes into cooler 110 (describedhereinafter).

The resulting concentrated ammonia-water-vapor from rectifier 76 ispassed through conduit 84 into conduit 86, which conduit is of course incommunication with juncture 20. Hence, conduit 86 contains therein thesecond stream S of coke oven gas. Thus, the second stream S now enrichedwith the ammonia vapor from conduit 84, is passed via exhaust fan 88through conduit 90 to the steam boiler 56.

It is important that, upon introduction of the concentratedammonia-water-vapor from conduit 84 into conduit 86, no condensation ofwater or other vapor occur. Accordingly, provision is made for a heater92 to heat the second stream S of coke oven gas at a point prior to theinjection of the ammonia-water-vapor therein. As shown in the drawing,heater 92 is supplied with steam from steam boiler 56 via conduit 94.

It is to be noted that in accordance with my invention, the amount ofcoke oven gas separated at juncture 20 and utilized as the first portionS will be slightly in excess of the normal fuel consumption of the cokeoven. That is, it will be slightly in excess of the heat requirementsfor the coke oven heating flues. Accordingly, a bleed-01f line 96 isprovided, one end of which communicates with conduit 44, the other endof which communicates with conduit 86. Regulating means, e.g., governor98, in the bleed-off line 96 automatically bleeds off that excess of gaspresent in the first stream S so that it is fed into the second streamof gas S in conduit 86.

Steam boiler 56 is maintained under conditions of elevated temperatureand pressure, typically at a temperature of at least about 1000 C., anddesirably at a temperature of about 1400 C., and at elevated pressures,e.g., of the order of from 40 to 100 atmospheres. Under theseconditions, the ammonia present in the second stream S is readilycracked to nitrogen and water, these products being non-pollutant to theatmosphere. In like manner, other contaminants present in stream 8; areconverted to relatively inert or non-pollutant products, so that theoverall products obtained in the steam boiler 56 may readily be ventedto the atmosphere as waste gases via stack 100.

It will be noted that provision is made for a water cooler 102. Make-upwater is supplied to the cooler via conduit 104. Cooled water exits fromcooler 102 via conduit 106, with warmer water that is to be recooledbeing returned via conduit 108.

Cool water from conduit 106 is fed into liquor cooler 110 via conduit112, the heated water being returned to conduit 108 via conduit 114. Inthe same manner, cool water is fed to cooler 61 via conduit 106, thewarmer water being returned to the cooler via conduit 108. And again,cooling for rectifier 76 is provided from cool water via conduits 106and 78, the warmer water being returned to water cooler 102 via conduits80 and 108.

As will be seen from the drawing, liquid media for the scrubber 38 issupplied not only via fresh water from conduit 42, but also byrecirculation of some of the aqueous ammoniacal liquor at the bottom ofthe scrubber. Thus, a portion of this liquor is withdrawn via conduit109, cooled by cooler 110, and recycled to spray head 111. Similarly,ammoniacal liquor from flanges 113 and 115 is collected in conduits 117and 119, respectively, and recycled to spray heads 121 and 123.

Considering an illustrative example of the foregoing method andapparatus in actual operation, coke oven gas produced in the coke ovenfrom the coking of coal will generally enter conduit 16 at a temperatureof from about 700 to 800 C., the gas having a dew point of about 68 C.As the gas goes along conduit 16 it cools down to about 600 C. prior toentering cooling chamber 18. The spraying of droplets of ammonia liquorfrom flushing liquor tank 118 into cooling chamber 18 cools the gas sothat upon leaving the cooling chamber and passing to juncture 20 the gasis cooled down to a temperature of, e.g., about 90 C., and has a dewpoint of about 78 C.

The first stream S of the gas thus enters spray cooler 26 at atemperature of about 90 C. Ammonia liquor entering spray cooler 26through spray head 63 is typically at a temperature of about 35 C. Cokeoven gas, after leaving cooler 26 via conduit 28 and passing through tarfilter 30 and exhaust fan 34, has a temperature of about 48 C. and a dewpoint of about 38 C. The gas then passes through scrubber 38 and leavesthe scrubber at a temperature of about 40 C. The thus cleansed gaspasses via line 44 into distribution channel 46 for combustion in thecoke oven heating flues.

Considering the second stream S of coke oven gas, as previously noted,this stream passes through conduit 86 and then through conduit 90 intothe steam boiler 56. Typically, it reaches the steam boiler at atemperature of from about 100 to 110 C. with a dew point of about 80 C.

Referring to scrubber 38, fresh water is fed via conduit 42 andgenerally is introduced at a temperature of about 35 to 38 C. Thetemperature of the ammonia liquor existing from the scrubber 38 viaconduit 70 is typically about 39 C. That portion of liquor that is to berecirculated through scrubber 38 via conduit 109 is cooled via cooler110, e.g., to a temperature of 38 C.

Ammonia liquor is also collected from the bottom of spray cooler 26.This ammonia liquor is passed to tank 118, generally at a temperature offrom about 40 to 50 C. Part of the ammonia liquor from the bottom ofspray cooler 26 is recycled. Thus, it leaves via conduit 59 at atemperature of about 50 C., is cooled by cooler 61 to a temperature ofabout 35 C., and is recycled through spray head 63.

Tar-free ammonia liquor is passed through conduit 60, generally at atemperature of from about 50 to 70 C., and is introduced todephenolizing column 62. Upon exiting from the dephenolizing column(through conduit 66) the temperature of such ammonia liquor is generallyof the order of about 50 C. Thus, ammonia liquor exiting from thedephenolizing column (conduit 66) and from the scrubber (conduit 70),when combined together typically are at a temperature of from about 40to 45 C. This stream is passed to distilling column 72. Dephenolizedwaste water at about 98 C. is drawn ofl from the bottom of the columnvia conduit 82. Ammoniawater vapor is evolved at the top of the column,typically made up of about 92% water and 8% ammonia at a temperature ofabout 98 C. The vapor then passes into rectifier 76 for concentration,and emerges from the rectifier with an ammonia concentration of about 10to and a water vapor concentration of from about 85 to 90%, thetemperature being about 95 C.

It is important that when this ammonia-water vapor is admixed with the(uncleansed) second stream S of coke oven gas, no vapor condensation,e.g., of ammonia, water vapor, or the like, occur. Accordingly, heater92 is disposed so as to preheat stream S prior to the addition theretoof ammonia-water vapor from conduit 84. Steam for heater 92 is providedvia conduit 94 from steam boiler 56. Thus, stream S is typically at atemperature of 90 C. (dew point 78 C.) prior to entering heater 92 andexits from the heater at a temperature of from about 110 to 120 C. Thiseffectively prevents vapor condensation when ammonia-water vapor fromconduit 84 is admixed with preheated stream S Referring to water cooler102, it is desirable that the cool water therefrom entering conduit 106be at a temperature of below 30 C. Thus, water entering liquor cooler110 via conduit 112 is at about 30 C., the warmer exit water leaving viaconduit 114 typically being about 34 C. Similarly, the water enteringcooler 61 via conduit 106 is at about 30 C., the exit Water leaving viaconduit 108 being at about 45 C. In like manner, water enteringrectifier 76 via conduit 78 is at 30 C., the exit water being a fewdegrees higher. The warmer water returning to cooler 102 via conduit 108is generally of a temperature of from about 40 to 45 C.

Stream S now passes via conduit to steam boiler 56, typically at atemperature of about to C. (dew point 80 C.). The steam boiler isdesirably at about 1400 C. with a pressure of about 100 atmospheres.Accordingly, at these relatively drastic conditions ammonia is readilycracked to nitrogen and water. Other contaminants that would tend topollute the atmosphere are similarly cracked or converted tosubstantially non-pollutant materials. The resulting waste gases arethen vented to the atmosphere through stack 100. The exit gases aregenerally at a temperature of about 200 C. (dew point of about 70 C.).

It will be apparent that the foregoing method and apparatus providesmeans for utilizing a portion of coke oven gas evolved in the coking ofcoal to satisfy the heat requirements of the coke oven heating filues.The remaining portion of coke oven gas may readily be passed to a steamboiler for conversion of atmospheric contaminants to nonpollutants,e.g., cracking of ammonia to nitrogen and water, followed by venting tothe atmosphere, whereby little or no atmospheric pollutants areintroduced. My process provides for merely cleaning approximately thatportion of the coke oven gas that is needed to satisfy the fuelrequirements of the coke oven. The remaining portion need not besubjected to cleaning. Additionally, the objectionable contaminantsinitially present in that portion of the coke oven gas that is to becleansed are separated, passed into that portion that has not beencleansed, and then converted to substantially non-pollutant byproducts.

The commercial operation of my method is advantageous. Thus, consideringa typical coke oven, approximately 10,000 tons per day of coking coalare utilized along with approximately 6,500 tons per day of fresh water,the electric requirements being approximately 100 mw.h. per day. Theresulting products are coke in the amount of about 7500 tons per day,steam (for power generation) in the amount of about 12,000 tons per day,and dephenolized waste water in the amount of about 2,000 tons per day.All waste gases are passed to the stacks and vented directly to theatmosphere.

Variations can, of course, be made without departing from the spirit andscope of my invention.

Having thus described my invention, what I desire to secure and herebyclaim by Letters Patent is:

1. In a method of processing a stream of coke oven gas containingvaporous tars, ammonia, and water therein, said gas having been obtainedfrom a coke oven battery comprising a plurality of spaced apart: cokingchambers with a plurality of heating walls disposed therebetween, saidheating walls each having therein a plurality of heating flues,comprising:

( 1) dividing the stream of coke oven gas into a first stream forsubsequent combustion in the coke oven heating lines and a second streamfor subsequent conversion to waste gases,

(2) cooling the said first stream to condense water vapor and tar vaportherein and thereby form aqueous ammonia liquor and tar,

(3) scrubbing said cooled stream with aqueous media to cleanse the gasand remove the ammonia therefrom, thereby forming aqueous ammonialiquor, and

(4) distilling the aqueous ammonia liquors, formed by cooling the gas instep (2) and scrubbing the gas in step (3), to form ammonia vapor theimprovement comprising (a) admixing said ammonia vapor with the secondstream of coke oven gas and passing the ammonia rich second stream to aconversion zone and converting the stream to waste gas which may bevented to the atmosphere and (b) passing the cleansed first stream tothe heating flues and burning the stream therein to provide heat fordestructive distillation of coal in the coking chambers.

2. The method of claim 1 wherein the amount of coke oven gas employed inthe first stream i slightly in excess of the heating requirements forthe heating flues of the coke oven battery.

3. The method of claim 2 wherein prior to passing the cleansed firststream to the heating flues, that amount of gas in excess of the heatingrequirements for the heating flues is bled off and admixed with thesecond stream prior to its conversion to waste gases.

4. The method of claim 1 wherein at least a portion of the aqueousammonia liquor formed from the spray cooling step (2) is employed in thescrubbing step (3).

5. The method of claim 1 wherein distilling step (4) is carried out withsteam to form said ammonia-water vapor, said vapor then being cooled toincrease the ammonia concentration therein, said cooling being effectedprior to the admixing of the ammonia vapor with the second stream ofgas.

6. The method of claim 5 wherein said second stream of gas is heatedprior to the admixing of ammonia vapor therewith, said heating being tosuch temperature that upon said admixing, water or tar that may bepresent in said vapor does not condense.

7- The method of claim 1 wherein the scrubbing step (3) is performed ina plurality of stages and wherein there is employed in the scrubbing (a)fresh water, (b) recycled ammonia liquor from the scrubbing, and (c)ammonia liquor obtained from cooling step (2), the amount of recycledammonia liquor (b) and ammonia liquor (c) being greater than the amountof fresh water (a) employed.

8. Apparatus for cleaning and combusting coke oven gas comprising:

(a) means for dividing coke oven gas containing ammonia therein into afirst stream for subsequent combustion in coke oven heating flues and asecond stream for subsequent conversion to waste gases,

(b) means for scrubbing said first stream with aqueous media to cleansethe gas and for recovering ammonia therefrom as aqueous ammonia liquor,

(c) conduit means for passing the first stream to said scrubbing means,and

(d) conduit means for passing the cleansed first stream to coke ovenheating flues for combustion therein.

9. The apparatus of claim 8 additionally comprising:

(e) conduit means for passing aqueous ammonia liquor formed in element(b) to a distilling means,

(f) means for distilling the aqueous ammonia liquor and for recoveringammonia vapor,

(g) means for converting the second stream to waste gases and forventing such gases to the atmosphere,

(h) conduit means for passing the second stream to said convertingmeans, and

(i) conduit means for passing the ammonia vapor formed in element (f) tosaid conduit means defined in element (b) so that such ammonia vapor isadmixed with the second stream prior to its combustion.

10. The apparatus of claim 9 additionally comprising:

(i) conduit mean communicating with said conduit means defined inelement (d) and communicating with said conduit means defined in element(h), and

(k) means for proportioning the flow of cleansed gas (1) to the cokeoven heating flues and (2) through said conduit means defined in element(j) such that that portion of cleansed gas in excess of the heatingrequirements of the heating flues is passed through said conduit meansdefined in element (j).

References Cited UNITED STATES PATENTS NORMAN YUDKOFF, Primary Examiner.

D. EDWARDS, Assistant Examiner.

US. Cl. X.R.

